Light emitting diode replacement lamp

ABSTRACT

Thermal management and control techniques for light emitting diode and other incandescent replacement light technologies using a current controller are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation-in Part of copendingapplication No. 10/820,930 filed Apr. 8, 2004; application No.10/893,727 filed Jul. 16, 2004; and application No. 11/868,406 filedOct. 5, 2007. Applications Nos. 10/893,727 and 11/848,406 claim priorityfrom Provisional Application 60/517,130 filed Nov. 4, 2003 andapplication No. 10/820,930 claims priority from Provisional Application60/502,495 filed on Sep. 12, 2003. All of the aforementioned patentapplications, from which this patent application claims priority, areincorporated herein by reference in their entire.

BACKGROUND

1. Field of the Invention

The present invention relates to a light emitting diode (LED)illumination device and method and more specifically to a light emittingdiode, integrated with electronic circuitry.

2. Description of Related Art

Currently lighting applications are dominated by incandescent lightingproducts. Because they use hot filaments, these products produceconsiderable heat, which is wasted, in addition to visible light that isdesired. Halogen based lighting enables filaments to operate at a highertemperature without premature failure, but again considerablenon-visible infrared light is emitted that must be disposed of. This isconventionally done by using a dichroic reflector shade thatpreferentially passes the infrared as well as a portion of the visiblelight. The nature of this dichroic reflector is such that it passesseveral different visible colors as well as the infrared radiation,giving a somewhat pleasing appearance. This has lead to numerousapplications for the halogen lights in which the entire light is usedfor decorative purposes. These lights consume substantial current anddissipate considerable unwanted heat. These bulbs are designed tooperate at a variety of voltages between 12 Volts to as high 115Volts orgreater.

Light emitting diodes have operating advantages compared to ordinaryincandescent as well as halogen lights. LEDs can emit in a narrow rangeof wavelengths so that their entire radiant energy is comprised within apredetermined range of wavelengths, eliminating, to a large degree,wasted energy. By combining light colors white can be created. Becausesuch LEDs can now emit in the ultraviolet, the emitted radiation canalso be used to excite a phosphor to create white light and other hues.

LEDs have an extremely long life compared to incandescent and halogenbulbs. Whereas incandescent and halogen bulbs may have a life expectancyof 2000 hours before the filament fails, LEDs may last as long as100,000 hours, and 5,000 hours is fairly typical. Moreover, unlikeincandescent and halogen bulbs, LEDs are not shock-sensitive and canwithstand large forces without failure, while the hot filament of anincandescent or halogen bulb is prone to rupture.

Halogen bulbs, incandescent bulbs, and LEDs all require a fixedoperating voltage and current for optimal performance. Too high anoperating voltage causes premature failure, while too low an operatingvoltage or current reduces light output. Also, the color of incandescentand halogen lights shifts toward the red end of the visible spectrum ascurrent and voltage are reduced. This is in contrast to LEDs, in whichonly the intensity of the light is reduced. Furthermore, as the voltageto an incandescent and halogen light is reduced, its temperature drops,and so its internal resistance decreases, leading to higher currentconsumption, but without commensurate light output. In cases wherebatteries are used as the source of energy, they can be drained withoutproducing visible light.

Incandescent and halogen bulbs require a substantial volume of space tocontain the vacuum required to prevent air from destroying the filamentand to keep the glass or silica envelope from overheating and toinsulate nearby objects from the damaging heat. In contrast, LEDs, beingsolid state devices, require much less space and generate much lessheat. If the volume of an incandescent or halogen bulb is allocated to asolid state LED light, considerably more functions can be incorporatedinto the lighting product.

Unlike incandescent and halogen lights, LEDs ordinarily produce light ina narrow, well defined beam. While this is desirable for manyapplications, the broad area illumination afforded by incandescent andhalogen lights are also often preferred. This is not easily accomplishedusing LEDs. The light produced by incandescent and halogen lights thatis not directed towards the target performs a useful function byproviding ancillary illumination and a decorative function. Halogenlights with their dichroic reflectors do this unintentionally, butordinary incandescent lights employ external shades, not part of thelight bulb, in a variety of artistic designs to make use of thisotherwise misdirected light.

LEDs are advantageous in that they consume far less electrical powerthan incandescent lights, on the order of one-sixth as much power, for agiven light output. However, LEDs are subject to thermal damage ordestruction at temperatures that are much lower than those tolerated byincandescent bulbs. LEDs are damaged at temperatures exceeding about 150degrees Centigrade (423° K). This is in contrast to typical incandescentbulbs that typically operate at 3000 to 6000° K.

Additionally, incandescent bulbs are self regulating by increasing theinternal resistance of the bulb as power to the bulb is increased. Thislimits the amount of current that flows through the bulb and maintainsthe bulb within an operating temperature range that is non-destructive.On the other hand, LEDs are subject to a thermal runaway condition inwhich excessive power causes the LED to heat and lower the LED internalresistance, which causes more current to flow and more heating to occur.This thermal runaway can cause the operating life of the LED to beseverely shortened or may lead to the rapid destruction of the LED.

LEDs can only operate over a relatively narrow operating voltage,typically from about 2 to 4 Volts. Most power sources provide a voltagethat is not in the range needed to safely drive the LEDs. Because ofthis, voltage regulation is required to convert the range of availableline voltages, and in some instances battery voltages, into levels thatare useful for powering the LEDs.

Voltage regulation is accomplished using electronic circuitry, such assurface mounted electrical components that are mounted to a printedcircuit board (PCB). These electrical components can be installed on thePCB along with the LEDs. PCBs are usually made of alternating layers ofinsulating materials such as fiberglass and copper foil for formingcomplex circuits. These types of PCBs typically do not efficientlyconduct the heat generated by the electrical components and LEDs awayfrom the LEDs. Metal core boards made with aluminum are more efficientat conducting heat away from the LEDs, however these boards are muchmore expensive and are limited to a single side to contain circuitry.Typical metal core boards and fiberglass/copper PCBs used for highdensity LED light applications do not have sufficient heat conductingcapacities to dissipate more than about 1 Watt away from LEDs. Failureto control the heat at the LEDs can lead to the thermal runaway andsubsequent damage of the LEDs.

Dimming LEDs, cold cathode fluorescents and other non-incandescentlighting traditionally involves complex circuits using microprocessors.Most conventional incandescent dimmer controls affect the dimmingfunction by reducing line voltage supplied to the fixture. LED and CFLcircuits typically contain regulating circuits to convert incoming linevoltage power, typically 110VAC in the United States, to avoltage/current that is suitable for the LED or CFL. Modulating the linevoltage with a conventional dimming circuit does not produce the desireddimming effect on LED and CFL lighting because of the regulatingcircuits.

One traditional approach to produce dimming capabilities withconventional dimmer switches is to use a microprocessor andanalog-to-digital converter (ADC) to sense incoming voltage and tocontrol the regulated circuit such that the perceived result isequivalent to the dimming of a conventional incandescent bulb. In thesecircuits, the ADC allows the processor to read the incoming voltage, andthe processor then produces a pulse wave modulated (PWM) waveform thatmodulates a control or sensing signal to the power regulator to reducethe resulting brightness responsive to the modulation. Many power ICsdesigned for lighting applications provide “dimming” control pinsspecifically for the purpose of allowing for digital control of thebrightness in regulators based on those ICs.

It is submitted that microprocessor based dimming controllers addunnecessary expense and complexity to LED lighting systems. Themicroprocessors are also subject to heat from the LEDs which can affectthe reliability of the circuits.

SUMMARY OF THE INVENTION

The present invention overcomes the limitations of halogen orincandescent light sources, and combines their desirable properties withthe advantages afforded by LEDs into a unique system and productintended for general illumination purposes.

An embodiment of the present invention may therefore comprise an LEDlamp that is capable of replacing standard incandescent and halogenbulbs for a wide variety of purposes. The functionality of this lightingsystem will go well beyond what is available in ordinary incandescentand halogen lights. Note that standard bulbs frequently are used infixtures which provide two functions: direct lighting and decorativelighting. The decorative lighting in particular is often associated witha shade, which may alter various properties of some or all theillumination, some of which may be superfluous to the directillumination function.

This embodiment will contain an electrical connector or base the same asor equivalent to the standard bulb base, a printed circuit board (orother circuit substrate or module) electrically connected to the base, adriving circuit that is mounted on or embodied by the printed circuitboard, and one or more LEDs of one or more colors attached to theprinted circuit board. The driving circuit comprises a solid statecircuit that regulates the voltage and current available from the sourceand regulates the output to the constant value required for the LEDs.The available source voltage can be either above or below that requiredby the LEDs.

An additional embodiment to the present invention may also comprise anLED lamp that replaces incandescent and halogen lamps as well as theirdecorative shades by including LEDs on both sides of the printed circuit(PC) board, where the LEDs are on the opposite side of that intended fordirect illumination and where they provide the decorative function.These LEDs may provide a decorative function by illuminating thebuilt-in envelope or shade around the lamp.

An additional embodiment to the present invention may include additionalcircuitry occupying the volume available. This circuitry may include thefollowing: circuitry to allow remote control of lighting functions viaan infrared or wireless device; circuitry to change the color of eitheror both of the (decorative) shade illumination and the directillumination LEDs; circuitry that causes a time variant color and orintensity to the (decorative) shade illumination and/or the directillumination; circuitry that allows the external switching viamechanical action of color, pattern or intensity on either the shade ordirect illumination; circuitry that enables the switching of the variousfunctions of color, intensity, pattern by interrupting the power to thecircuit within a predetermined time interval.

An additional embodiment to the present invention may include mechanicalactuators that alter the pattern and color of light to the shade for thepurpose of decorative illumination. This may include a mechanical methodsuch as a shadow screen, multi-faceted mirror or other reflective ordiffractive optical component or components either fixed within theenvelope of the lighting unit, or provided with a means of moving theinternal components to vary the pattern and or color of the resultinglight for decorative or functional purposes.

Another embodiment involves a method for regulating current drivethrough at least one light emitting diode to compensate for temperatureinduced resistance changes in the light emitting diode. The methodincludes supplying a source voltage and using the source voltage tocreate a regulated current that is usable by the light emitting diode.The regulated current is applied to the light emitting diode to causethe regulated current to flow through the light emitting diode. A sensevoltage is generated that is related to the regulated current and to atemperature at a position in a thermal pathway of heat emanating fromthe light emitting diode. The heat is produced by the light emittingdiode responsive to the regulated current. The sense voltage is used asa feedback to modify the regulated current to be maintained within anon-destructive operating range of the light emitting diode when theregulated current would otherwise be outside of the non-destructiverange due to a decreased resistance of the light emitting diode causedby an increased temperature of the light emitting diode.

Another embodiment involves a current regulator for regulating currentthrough at least one light emitting diode to compensate for temperatureinduced resistance changes in the light emitting diode. The currentregulator includes a source voltage that is connected to a voltageregulator. The voltage regulator is used for regulating the sourcevoltage to create the regulated current and for connection to the lightemitting diode to cause the current to flow through the light emittingdiode. The current regulator also includes a sense voltage generator forgenerating a sense voltage that is related to the current and to atemperature at a position in a thermal pathway of heat emanating fromthe light emitting diode. The sense voltage is used as a feedback tomodify the regulated current to be maintained within a non-destructiveoperating range of the light emitting diode when the regulated currentwould otherwise be outside of the non-destructive range due to adecreased resistance of the light emitting diode caused by an increasedtemperature of the light emitting diode.

Another embodiment involves a method for removing heat from at least onehigh power light emitting diode having an integral metal slug fortransferring heat away from the light emitting diode. A printed circuitboard is configured to electrically connect to the light emitting diodeto generate light. At least one via is arranged in the printed circuitboard in a location to contact the metal slug to transfer heat from thelight emitting diode through the metal slug to the via. A heat sink isarranged in thermal communication with the via to receive heat from thevia and to transfer the heat to the ambient environment.

Yet another embodiment involves an arrangement for removing heat from atleast one high power light emitting diode having an integral metal slugfor transferring heat away from the light emitting diode. A printedcircuit board is electrically connected to cause the light emittingdiode to generate light. At least one thermally conductive via in theprinted circuit board is positioned in a location that is in thermalcommunication with the metal slug. A heat sink receives heat from thevia and transfers the heat to the ambient environment.

Another embodiment involves a method for removing heat from at least onehigh power light emitting diode having an integral metal slug fortransferring heat away from the light emitting diode. A printed circuitboard is configured to electrically connect to the light emitting diodeto generate light. The printed circuit board is arranged to define ahole adjacent to the metal slug. A heat sink is connected to the metalslug through the hole in the circuit board to transfer heat from thelight emitting diode to the ambient environment.

Another embodiment involves an arrangement for removing heat from atleast one high power light emitting diode having an integral metal slugfor transferring heat away from the light emitting diode. Thearrangement includes a printed circuit board that is electricallyconnected to the light emitting diode to generate light. The printedcircuit board defines a hole adjacent to the metal slug. A heat sink isconnected to the metal slug through the hole for transferring heat fromthe light emitting diode to the ambient environment.

Another embodiment involves a method of dimming at least one lightemitting diode. A source voltage is supplied and is regulated to createa regulated voltage that is within a voltage range which is usable bythe light emitting diode. The regulated voltage is controlled throughfeedback that is at least partially based on the source voltage suchthat a change in the source voltage produces a predetermined change inthe regulated voltage.

Another embodiment involves a dimmer apparatus for use in dimming atleast one light emitting diode. A voltage regulator receives a sourcevoltage that is not in a range that is usable by the light emittingdiode and receives a feedback signal. The voltage regulator generates aregulated voltage that is within a voltage range that is usable by thelight emitting diode. The regulated voltage is generated at a level thatis at least partially determined by the feedback signal. A feedbackcontroller creates the feedback signal based at least in part on thesource voltage such that a change in the source voltage produces apredetermined change in the regulated voltage.

An additional embodiment of the present invention may comprise themethod or methods for accomplishing the above-mentioned attributes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of the current state-of-the-art halogenillumination device referred to commonly as an MR-16.

FIG. 2 illustrates an embodiment of the present invention that canretrofit the halogen illumination device and contains LEDs forillumination on one side and LEDs for direct illumination on the other.Circuitry to enable regulation and other features is also shown.

FIG. 3 illustrates an embodiment of the present invention in which highintensity LEDs are placed on both sides to produce shade illuminationand direct illumination. A switch and circuitry for changing theattributes of the lighting is also shown.

FIG. 4 illustrates another embodiment of the present invention in whicha movable, multifaceted mirror is included on the shade side of theillumination unit to provide a variable pattern on the shade.

FIG. 5 illustrates another embodiment of the present invention in whichan internal fixture containing apertures is included to patternillumination to the shade.

FIG. 6 illustrates a means for producing a series/parallel circuitcomprised of individual LED semiconductor chips on a circuit board thatresults in a high density lighting array.

FIG. 7 shows an embodiment of the high density LED array in which it iscoupled with an integrated lens array that is movable to producevariable directional lighting.

FIG. 8 is a constant current implementation of a compact dc/dc boostconverter with a feature that enables current regulation of the LEDsbased on the thermal environment.

FIG. 9 is a compact constant current buck/boost circuit in which severalmethods that enable current regulation based on the thermal environmentare illustrated.

FIG. 10 illustrates one embodiment of a current regulator withtemperature dependent LED feedback.

FIG. 11 illustrates another embodiment of a current regulator withtemperature dependent LED feedback.

FIG. 12 illustrates an embodiment of a heat conducting apparatus forremoving heat from the LEDs.

FIG. 13 illustrates another embodiment of a heat conducting apparatusfor removing heat from the LEDs.

FIG. 14 an embodiment of a regulator circuit having a dimming function.

DETAILED DESCRIPTION OF THE INVENTION

While this invention is susceptible to embodiment in many differentforms, there are shown in the drawings, and will be described herein indetail, specific embodiments thereof with the understanding that thepresent disclosure is to be considered as an exemplification of theprinciples of the invention and is not to be limited to the specificembodiments described.

FIG. 1 illustrates an incandescent halogen type bulb commonly available.The features of this bulb have been derived from the operatingcharacteristics implicit in the operation of these type illuminationdevices: they operate at high temperatures; they require an evacuatedenvelope separated from the hot filament; they emit large quantities ofinfrared radiation experienced by the user as heat; and they consumelarge quantities of electrical power. Nonetheless these devices are incommon usage and fixtures and appliances have been constructed toaccommodate the form, fit, and function of these bulbs. This particularunit is a model MR-16.

FIG. 1 illustrates the incandescent halogen bulb and its essentialcomponents. These are a connector 101 that attaches to a standard sourceof electrical power which has a mating adapter; an evacuated transparentcapsule 102 containing the hot filament 105; an envelope 103 that actsas a shade and filter to allow infrared radiation to pass, whilereflecting a portion of the desirable visible light to the objectsbelow; a transparent front cover 104 that allows the radiation to pass,while protecting the evacuated capsule 102 from breakage.

In contrast to incandescent lights, LEDs consume less power, emit in anarrow beam, emit less heat, and can be formulated in a wide variety ofcolors both inside and outside the spectrum visible to humans. Becauseof these implicit differences, the use of LEDs creates opportunities toadd operation features to light bulbs, which heretofore were consideredsimple illumination devices. It is the object of this disclosure toenumerate unique features that will improve the usefulness of thelighting devices based on LEDs.

FIG. 2 illustrates the first embodiment of the current invention. Thisilluminating device is intended to have the same form fit and functionas the incandescent illumination device of FIG. 1 and as such has asimilar electrical connector 201 and similarly shaped transparent ortranslucent envelope 202. The envelope 202 will act to scatter lightemitted from inside the envelope and be visible from the outside. Assuch, the envelope 202 can serve as a screen onto which are projectedand displayed images, colors or other decorative orinformation-containing light either visible to humans or at shorter orlonger wavelengths. The content of this information is formulated bycircuitry contained on one or more circuit boards 206 contained withinthe envelope of the bulb 202. This circuit 206 in its simplest formcontrols other illumination devices such as the LEDs 207 also located onthe back of the circuit board 204. Another circuit 205 can be used tocontrol high power LEDs 209 in an array 208 located on the opposite sidefor direct illumination of objects outside the envelope of the lightingdevice. However, this circuit or circuits may enable several usefulfeatures. These are:

1. A timer to adjust the color and illumination level according to somepreset or user-adjustable schedule.

2. A photocell to turn on or off the light depending on the ambientlight level and or a proximity sensor.

3. A signaling function that communicates with other lights

4. A switch that is user accessible that allows a switching ofillumination characteristics such intensity, color, continuous orflashing illumination modes.

Also located on circuit board 204 is a power conditioning circuit 205that regulates power to the high intensity LEDs 208 located on theunderside of the board. This circuit adapts and controls the poweravailable via the connector 201 and conducted to the board via wires203. The circuit 205 may contain storage features including a battery toenable the lighting device to act as an emergency light source in theevent of a power failure. The circuit may rectify ac power to dc to suitthe desired current and voltage required by the series and/or parallelarray of LEDs and provide power to other on-board circuitry.

In this embodiment, the LEDs 207 on the backside of the PC board 204 canserve the function of communication and or decoration. For decorativepurposes, the shade 202 will be made of a colored or white transparentor preferably translucent material such as plastic or glass which istextured so as to scatter light. In this manner light from the LEDs 207impinge on this surface and are made more visible to the user, and canserve the function of decoration. The shade 202 may also containpenetrations 210 to allow heat to exit the LED enclosure.

FIG. 3 illustrates a similar incandescent replacement product. Thisproduct also contains an electrical connector 301, a shaped translucentor transparent envelope 302 with holes 310 to remove heat, one or moreprinted circuit boards 304 within the enclosure, means such as wires 303to conduct electrical power to these board(s), the product now has highintensity illumination LEDs 307 on the top surface and other highintensity LEDs 309 in an array 308 on the bottom surface. Unlike theproduct of FIG. 2 which had small LEDs with a narrow exit beam and lowintensity, these high intensity LEDs 309 and 307 have a higher lightoutput generally greater than 10 lumens and the exit angle of the lightmay range from a narrow angle to a very broad beam as desired. Tocontrol these LEDs additional circuitry may be required as shown in thefigure. In addition to the power transforming circuit 305, and thecontrol circuits 306, additional power handling circuits 311 may benecessary. These high power LEDs may have one or more colored lightoutputs other than white, and have different orientations other thanvertical to provide decorative illumination above the lighting product.A switch 311 that is accessible by the user can be used to controlcharacteristics of operation of the lighting product.

FIG. 4 illustrates another embodiment of the product. Unlike theprevious examples in which modification of the color, intensity andpattern took place by electrically controlling the electrical power toindividual devices of one or more orientations and color, this productcontains a mechanical method for varying the intensity, and pattern withtime. This is accomplished for example using a multi-faceted mirror 420,operated by a miniature electric motor 421 that changes the orientationand position of the mirror. In this way light is reflected or diffractedto form a pattern of shapes and color on the translucent or transparentenvelope 402.

FIG. 5 illustrates another embodiment in which is added the feature of apatterned mask 520 that casts a shadow or other optical means apredetermined pattern by blocking or otherwise modifying the pattern oflight emanating from the internal LEDs 507 located on the back side ofthe circuit board 504. Other features from other embodiments discussedalready may also be incorporated.

It may be appreciated from these descriptions that the LEDs used inthese embodiments, though small, occupy considerable space that limitsthe overall light output of the product. This is due to the need toprovide electrical connections to each of the semiconductor lightemitting chips that are housed in large packages that provide bothelectrical connections and a means for removing heat and permit theexiting of useful light. The packages also often contain a lens ormirror for shaping and directing this light. While these packages allowsome freedom of use, they also limit the density and eliminate the meansto provide the integration of the functions of heat dissipation, lightdirection and electrical connection by independent means. Many of thesefunctions could be accommodated within a printed circuit board ofappropriate design for a group of devices at the same time and withinthe circuit as it is formed.

One means of improving the light density of the overall product is toincorporate the light emitting dies onto a suitable patterned circuitboard that contains the external circuitry needed to power and connectthe LED devices without the excess baggage of a package. FIG. 6illustrates such an arrangement. The embodiment consists of a printedcircuit board comprised of at least a middle portion 601 that may be theusual fiberglass core or one that contains metals, ceramics or othermaterials to enhance thermal conductivity, a top metal clad layer 603and a bottom cladding layer 602. It should be well understood that thesetop and bottom layers can easily be patterned by such processes asetching. A light emitting assembly can be attached to the patternedsurface of cladding 603 by cementing with a thermally and electricallyconducting compound or by welding or some other method. Then thecladding 603 may act as either or both a thermal and electricalconducting pathway. The light emitting assembly consists of a metal base604 to which is bonded a semiconductor light emitting chip 605. Thislight emitting chip contains a pn junction that emits light andconducting top and bottom surface layers for electrical and thermalcontact. A conducting wire or tab connects the top conducting member ofthe junction to the opposite conducting pad on the next assembly, thusbuilding up a circuit that is in series. Using a different connectionscheme, but the same general method, a parallel connection can beassembled. By doing this, a relatively dense build-up of light emittingchips can be assembled using the thermal and electrical transfercharacteristics of the printed circuit board. Furthermore, heat sinking,cooling or other components can be attached to the board, improvingperformance, for example on the back side 602 of the printed circuitboard. Although not shown, it should be understood that this connectionmethod can be extended in the two dimensions of the plane of the board.

Such chips as illustrated in FIG. 6 will emit light in all directions.Such a distribution of light may not be desired for any lightingapplications. Therefore, a matching array of lens that is positionedover the light emitting chips would be desirable. This separation of thetop lens array from the LEDs is desirable as it allows the lens array tobe positioned independently, allowing the light directed by the lens tobe moved and/or focused by moving the lens array in the threedimensions. The movement can be controlled via a variety of methods suchas stepper motors or piezoelectric activated motion controllers whosesupport electronics is also contained on the printed circuit board. Thearray of lenses can be molded from a transparent clear or coloredmaterial with a variety of spherical or hemi-spherical shapes.

FIG. 7 illustrates such an arrangement. The PC board 701 containingpatterned metal traces 703 has located on its surface light emittingportions consisting of semiconductor light emitting devices 705 that aremounted on bases 704. These areas are bonded together with electricallyconducting wires or strips to form a series/parallel circuit. Positionedover the top of these light emitting regions is a lens array 710 intowhich have been formed by a method such molding, a matching series ofoptical elements. Three such elements of two different shapes labeled711 and 712 are shown. This lens array 710 is spaced apart from thesemiconductor array and mounted in such a manner that it can beexternally manipulated in one or more of the three dimensions as shownby the opposing pairs of arrows. Hence, by moving the lens array, thelight emitted from the matching LED array can be directed and focused asrequired, in essence steering the light beam. This can be controlled byonboard electronics, and via remote control or such other means asrequired such as proximity sensors, timers and the like.

These lighting products require a source of alternating (ac) or directcurrent (dc). Although LEDs utilize direct current, it is possible touse the LEDs to rectify ac power provided the number of LEDs is chosento match the ac voltage. It is well understood how to transform ac powerto dc via a variety of well-established methods. The use of dc power assupplied by batteries however, presents some problems because as thebattery voltage declines under load, the current drawn by the LEDsrapidly declines, owing to the extremely non-linear current-voltagecharacteristic inherent in a diode. Since the light output of a LED isdirectly proportional to current, this means the light output rapidlydeclines. On the other hand, if battery voltage exceeds a predeterminedlevel, heating of the semiconductor junction that comprises the LED isexcessive and can destroy the device. Moreover, excess heat in the LEDjunction causes a condition called thermal runaway, in which the heatraises the current drawn at a given voltage, leading to further heating,which in turn leads to greater current draw and quickly destroys thedevice. This is especially a problem with high power LEDs and requirescareful thermal management.

In order to help avoid this problem it is useful to fix the currentthrough the LEDs rather than the voltage. Using a battery as the sourceof current however presents a problem because of the differing voltageand current behavior of the battery power source and the LED load.Therefore, a circuit is desired to regulate and fix the currentindependent of the voltage supplied by the battery. In the case wherethe battery voltage is less than the load voltage required by the seriesand/or parallel LED circuit, a boost circuit can be used as pictured inFIGS. 8 a and 8 b. In this circuit an integrated circuit device, IC1 801is used to control the charging and discharging of an inductor L1 803.This integrated circuit may be one of several that are available such asthe Texas Instruments TPS61040. After a charging cycle, the IC switchesthe circuit so that the inductor L1 803 is permitted to dischargethrough the load, which in this case is the light emitting diodes 805.The current is controlled via a feedback resistor R1 806. The value ofthe resistor is chosen to fix the maximum current that is permitted toflow through the load, which in this case, is one or more LEDs (LED1,LED2) shown as 805. This manner of control occurs because the voltagedrop across R1 806 is compared to an internally generated referencevoltage at pin FB of IC1 801. When the two voltages are equal thecurrent is considered fixed and will be controlled to that predeterminedvalue. A diode D3 802 is used to ensure protection of the IC1 801 incase the battery source (not shown) is connected backwards. The diode804 allows current flow through the LEDs 805 in only the forward, orlight emitting direction. In this invention, such a circuit would beenclosed within the envelope of the bulb.

FIG. 8 b differs from FIG. 8 a in that it builds into the circuit aneasy and inexpensive means of protecting the LEDs from excessive currentflow and the runaway that results from high temperatures. In thiscircuit a resistor with a positive resistance rate of change withtemperature, R2 807 is placed in series with a fixed resistor. ResistorR2 is physically located on the circuit board so as to be placed in thethermal pathway of heat emanating from the LEDs 805. Therefore, when thetemperature of the LEDs 805 increases, the resistance of R2 807 alsoincreases, and its resistance is added to that of R1 806. Since thevoltage drop across these combined resistances appears on the feedbackpin FB of IC1 801, the increased voltage is interpreted as a request fordecreased current. Hence, the natural tendency of the LEDs 805 to drawmore current that would ordinarily lead to the failure of the part isaverted by introducing a self-limiting control function.

This circuit has the advantage of being very efficient and compact andhaving built into it a temperature regulation that allows the resultingsystem to automatically adapt to the thermal environment in which it isplaced. Because of these attributes, it can, for example be put into aminiature lamp base of the kind used for flashlights (PR type flangebase).

However, the remaining limitation of the circuit is that it can onlyboost voltage from a lower value to a higher value required by the LEDload. Therefore, in situations where only one LED is required, but ahigher input voltage is all that is available, the excess voltage willappear across the LED even if the circuits in FIG. 8 are used. This willcause an excessive current to be drawn, leading to premature failure ofthe LED and premature draining of the battery. To solve this problem werequire a circuit that is still compact enough to fit into a bulb orbulb base, and that is capable of either raising or lowering the outputvoltage above or below the voltage of the incoming battery or other dcsupply in order to maintain the desired current through the LED load.Hence this circuit would either boost the voltage if the input voltagewere lower than required by the LED or reduce the voltage if it werehigher than that required to sustain the necessary constant currentthrough the LED. It is understood that LED here may refer to one or moreLEDs in a series, parallel or series/parallel circuit. Furthermore,because of the deleterious effects of temperature, this circuit musthave the ability to regulate the current through the LED depending onthe ambient temperature. The ambient temperature may be determined bythe environment as well as heat dissipated by the circuit and the LED.

Such a circuit is disclosed in FIG. 9. This circuit utilizes a so-calledCuk converter that is ordinarily used as an inverting switching voltageregulator. Such a device inverts the polarity of the source voltage andregulates the output voltage depending on the values of a resistorbridge. In this invention, the inverter circuit has been altered in aunique fashion so that it acts to boost the voltage output or buck thevoltage input in order to maintain a constant current through the loadrepresented by one or more LEDs 905. The circuit incorporates anintegrated circuit IC1 901 such as the National Semiconductor LM2611 CukConverter or equivalent. In this circuit, IC1's internal transistor isclosed during the first cycle charging the inductor L1 902 from thebattery source indicated as Vbat. At the same time the capacitor C2 904charges inductor L2 903, while the output current to the LEDs 905 issupplied by inductor L2 903. In the next cycle the IC1 901 changes stateto permit the inductor L1 902 to charge capacitor C2 904 and L2 903 todischarge through the LEDs 905. The control of the charging power andcurrent through the load is performed by the resistor network consistingof R2 906 a and R3 907 a. The overall value of these resistors togetherwith the current passing through the LEDs 905 from ground, sets avoltage that appears on the feedback pin (FB) of IC1 901. Resistor 907 ahas a positive temperature coefficient so that its resistance increaseswith temperature.

Because of thermal effects such as heat dissipation by the LEDs, heatproduced by the IC1 or other circuit components and the ambientenvironmental conditions, the current must also be altered toaccommodate these changes. This is affected by a temperature dependentresistor R3. In FIG. 9 a, resistor R3 907 a has a positive temperaturecoefficient in which the resistance increases with temperature. Theadditive effect of the series circuit with R2 906 a means that astemperature rises, the overall resistance of the combination does also,leading to an increase in voltage drop. This in turn causes IC1 todecrease the output current to the LEDs 905. In FIG. 9 b the resistornetwork is comprised of resistors in parallel and series. In thisinstance, resistors R2 and R4 906 b, 908 are fixed and resistor R3 907 bis temperature dependent with a positive temperature coefficient. Theuse of a parallel arrangement allows a greater freedom of choice oftemperature dependence than a simple series arrangement.

Other embodiments of temperature dependent control of the power suppliedto LEDs are shown in FIGS. 10 and 11. A LED current controller 910, FIG.10, includes a temperature dependent feedback circuit 912. Feedbackcircuit 912 provides a sense voltage 948 that is dependent ontemperature at or near LED 914 to current controller 910. Thetemperature dependent feedback causes current controller 910 to regulateLED current 918 to LED 914 to maintain the current within a safeoperating range that will not damage the LED. The temperature dependentfeedback prevents the LED current from moving out of the safe operatingrange due to changes in resistance of the LED caused by changes intemperature. While FIGS. 10 and 11 illustrate concepts with only oneLED, it should be understood that these concepts are equally applicablefor use with multiple LEDs where the circuit can simultaneously drive aplurality of LEDs.

Current controller 910 includes a regulator IC 920, which can bearranged similar to the Cuk Converter shown in FIG. 9. Regulator IC 920in the present example includes a source voltage input 922 that isconnected to a source voltage 924. Source voltage 924 provides the powerfor the regulator and the LED and is also connected to a chip enable pin926 of the regulator. In the present example, source voltage 924 is a DCvoltage. A ground pin 928 of regulator IC 920 is connected to ground930. Capacitor 932 connects between source voltage 924 and ground 930 toreduce or eliminate AC voltage variations from source voltage 924. Asupply pin 927 provides controlled current to the LED as the drivecurrent of the LED. Temperature dependent feedback of the currentcontroller can also be applied to the controller shown in FIG. 8, exceptthat the light emitting diode must be reversed in this instance.

Regulator IC 920, such as the National Semiconductor LM2611, operates toboost or buck the source voltage to maintain the LED current within thesafe operating range of the particular LED used. Similar to theoperation described above, an internal transistor of regulator IC 920 isclosed during a first cycle to charge inductor 934 from source voltage924. At the same time, capacitor 936 charges an inductor 938 while LEDcurrent 918 is supplied by inductor 938 to LED 914. In the next cycle,regulator IC 920 changes state to permit inductor 934 to chargecapacitor 936 and to allow inductor 938 to discharge through LED 914.

The safe operating range or non-destructive range of the LED is a rangeof currents within which the LED is designed to operate without thetemperature of the LED exceeding the temperature at which the LED isdamaged. By reducing the current to the LED, the temperature of the LEDcan be reduced or maintained below the damage temperature of the LED.The damaging temperature of the LED, and the non-destructive currentrange that maintains the LED below the damaging temperature, can bedetermined based on the circuit that the LED is connected with. Thedamaging temperature of the LED, or the safe operating temperature ofthe LED is typically available from the LED manufacturer.

In the present example diode 935 is connected between ground and a pointbetween capacitor 936 and inductor 938. Diode 935 acts as a switch tocontrol current flow to a single direction. Capacitor 937 is included inthe circuit to provide a filtering function to help maintain a constantvoltage and therefore current through the LED.

Regulator IC 920 includes a feedback pin 939 which is used forcontrolling the output at supply pin 927. Increased voltage at feedbackpin 939 is interpreted as a request for decreased current at supply pin927 and decreased voltage at feedback pin 939 is interpreted as arequest for increased current at supply pin 927.

Feedback circuit 912 includes an operational amplifier 940 that isconnected (not shown) to the source voltage and ground for power. Op amp940 produces sense voltage 948 as an output that is based on a inputvoltage 944 at a non-inverting (+) input and an amp feedback voltage 946at an inverting (−) input. Sense voltage 948 is connected to feedbackpin 939 of the regulator IC.

In the present example, a sense resistor 942 is connected between LED914 and the ground. Sense resistor 942 is also connected to thenon-inverting input of op amp 940. When LED current 918 flows throughsense resistor 942 sense voltage 944 is produced on the non-invertinginput of op amp 940. Input voltage 944 is proportional to the LEDcurrent in the present example because sense resistor 942 has a fixedresistance.

Amp feedback voltage 948 results at least in part from the use of atemperature dependent resistance. In feedback circuit 912, shown in FIG.10, the temperature dependent resistance is a thermistor 950 that has anegative temperature coefficient (NTC). NTC thermistor 950 is connectedin parallel with parallel resistor 952 and the parallel thermistor 950and resistor 952 are arranged in series with series resistor 954.Thermistor 950 and resistors 952 and 954 are arranged between theinverting input of op amp 940 and ground 930. An op amp feedbackresistor 956 is connected between the output and the inverting input ofthe op amp.

NTC thermistor 950 has a resistance that goes down as temperatureincreases. Decreased resistance, resulting from increased temperature,causes op amp 940 to have an increased gain in the configuration shownin FIG. 10. Sense voltage 948 increases when the gain of op amp 940increases.

Sense voltage 948 is connected to the feedback pin of the regulator ICthrough a low pass filter that includes a resistor 968 and capacitor970. The RC filter may slightly attenuate sense voltage 948. Since sensevoltage 948 is connected to the feedback pin of the regulator IC,increased sense voltage causes the regulator IC to produce a decrease inLED current.

Another feedback circuit 958, shown in FIG. 11, uses a thermistor 960that has a positive temperature coefficient (PTC) as the temperaturedependent resistance. Feedback circuit 958 is another example of acircuit that can be used for temperature dependent control of power toLEDs. Feedback circuit 958 can also be connected to a current controlleras described above and will therefore be discussed in conjunction with acurrent controller like the one shown in FIG. 10.

In the present example, LED 914 is connected between capacitor 937 and anon-inverting input (+) of an op amp 966. A LED current 972 flowsthrough the LED and a sense resistor 974 to cause the LED to emit light.LED current 972 flowing through sense resistor 974 creates an inputvoltage 976 at the non-inverting input of op amp 966.

PTC Thermistor 960 is connected in parallel with a parallel resistor 962and the thermistor 960 and resistor 962 are connected in series with aseries resistor 964. Thermistor 960 and resistors 962 and 964 arearranged in a feedback loop between the output and inverting input of opamp 966. A drain resistor 974 connects the inverting input of op amp 966to ground 930.

PTC thermistor 960 has a resistance that goes up as temperatureincreases and goes down as temperature decreases. In the arrangementshown in FIG. 11, increased resistance of PTC thermistor 960 resultingfrom increased temperatures causes an increase in sense voltage 978.Since sense voltage 978 is connected to feedback pin 939 of regulator IC920, through the low pass filter, the regulator IC responds bydecreasing current at supply pin 927 which reduces LED current 972.

In the examples shown in FIGS. 10 and 11, the simple resistor circuitshown in FIGS. 9 is replaced with a circuit that includes a relativelysmaller temperature sensitive component that controls feedback to thecurrent regulator. Because the absolute change in resistance of thetemperature sensitive component may be small, an amplifier is used toamplify the sense voltage across the temperature sensitive component toprovide adequate feedback to the current regulator.

In high current applications, the power loss through sense resistors R2807 (FIG. 8 b), R3 907 a (FIG. 9 a) and R3 907 b (FIG. 9 b) can become asignificant contributor to the heat generated by the system. Feedbackcontrollers 912 and 958 replace the single passive sense resistor inprevious embodiments with active circuits that use much smaller senseresistors that produce less heat.

Other temperature sensitive elements that exhibit a change in electricalcharacteristic as a function of temperature can also be used. Theseelements can be either active or passive and may require additionalcircuitry to provide adequate feedback. In some instances, in may benecessary to include additional circuitry around a temperature dependentcomponent in order to scale the temperature dependent changes to amagnitude that is useful for modifying the current sense voltage. Insome instances, such as the examples using the thermistor or a diode,the temperature dependent component may be placed in parallel and/orseries with one or more fixed resistors to bring the voltage and/orcurrent into a range that is useful in controlling feedback.

The temperature dependent resistance devices or other temperaturedependent elements are positioned in the thermal pathway of heatemanating from the LED. The temperature dependent device may be locatedin contact with the LED, either directly or through some other element.In these instances, the heat is conducted to the temperature dependentdevice before it is transferred to the air or atmosphere. In otherinstances, the thermal pathway to the temperature dependent device mayinclude air or some other fluid medium.

In some instances, a heat sink formed, for example, from a metal, isneeded to conduct heat away from high power LEDs to avoid damaging them.A high power LED 1000 is shown in FIG. 12 in partial cross sectionconnected to a printed circuit board (PCB) 1002 which includes circuitryfor powering the LED. High power LED 1000 has an integral metal slug1004 that contacts the light producing semiconductor die (not shown) ofthe LED. High power LEDs with integral metal slugs are known in the art.The metal slug facilitates the transfer of heat away from thesemiconductor because the metal slug has a low thermal resistance,typically about 5 to 10 degrees C/Watt. In conventional designs, unlikethe design of FIG. 12 which will be described in further detail below,the metal slug is connected to a metal pad on the PCB either directlywith solder or with another good thermal conductor. However, in manycases, conventionally connecting the metal slug to the PCB does notadequately remove the heat from the LED since the PCB is generally apoor thermal conductor.

Continuing with the description of the design of FIG. 12, a heatremoving arrangement 1006 is shown for removing the heat from the highpower LED. Accordingly, high power LED 1000 is connected to PCB 1002 toreceive power for operating. Arrangement 1006 has a number of platedthrough hole vias 1008. Plated thru hole vias are traditionally used toelectrically connect different levels of a circuit within a PCB or toinsert a leaded component that is later used for soldering to a circuitcomponent.

Through hole vias 1008 are used for conducting heat away from high powerLED 1000 to help to keep high power LED 1000 below a temperature atwhich the LED would be damaged from the heat. Vias 1008 extend throughthe PCB from metal slug 1004 to a heat sink 1010. The vias are thermallyconnected to the metal slug and heat sink to thermally communicate heatfrom the metal slug through the vias and the heat sink to the ambientenvironment. These thermal connections can be through contact alone, orthe connections may include a thermally conductive substance or physicalattachment.

Vias 1008 can be filled with a highly thermally conductive material suchas copper 1012, solder or other thermal compound. Vias 1008 can also beconnected to one or more layers of copper sheet 1014 that are part ofthe fiberglass PCB, in addition to being connected to the heat sink1010. In these instances, the copper sheet serves to facilitate heattransfer and dissipation.

Vias 1008 can be positioned in a high density arrangement by spacing thevias 0.050 inches or less on center. The high density is used to createa high density of metal under and surrounding the metal slug. A highdensity of vias facilitates heat transfer to a greater extent than lowerdensities.

Heat sink 1010 can be an aluminum sheet or other structure or materialfor transferring heat to the atmosphere. Heat sink 1010 may have a shapewith a large surface area to facilitate the heat transfer. Heat sink1010 is connected to vias 1008 in a manner which promotes heat transferfrom the vias to the heat sink Arrow 1009 illustrates a path of heattransfer. Heat sink 1010 may be shaped to create recesses so thatelectronic parts can be accommodated on both sides of the PCB. Theserecesses would be arranged at locations away from the LED where theelectronic parts are located.

The temperature dependent resistance used in the temperature dependentfeedback circuit, such as those described above, can be mounted in thethermal pathway of the heat from the high power LED, for example, bymounting the temperature dependent resistance in thermal contact withcopper sheet 1014 or heat sink 1010. In this way, the temperaturedependent resistance can determine a temperature that is related to thetemperature of the high power LED for control purposes, such as thosedescribed above.

Another embodiment, shown in FIG. 13, involves a heat removingarrangement 1020 with a heat sink 1022 that has a main body 1024 andraised portions 1026. High power LEDs 1028 are mounted and electricallyconnected to a PCB 1030. The LEDs are positioned over holes 1032 definedin the PCB. Heat sink 1022 is positioned on the opposite side of PCB1030 from LEDs 1028 and raised portions 1026 extend through holes 1028to contact metal slugs (not shown) in the LEDs. A thermally conductingmaterial (thermal compound) is used to enhance thermal contact betweenthe LEDs and the heat sink.

In heat removing arrangement 1020, heat is conducted away from the LEDsthrough the metal slugs, through the raised portion of the heat sink, tothe main body of the heat sink The main body of the heat sink dissipatesthe heat to the ambient environment or surroundings. In the exampleshown in FIG. 13, three high wattage (greater than 3 Watts each) LEDsproducing a total of 600 lumens are placed in close proximity and areoperable at safe temperatures.

In one instance, raised portions 1026 have a height above main body 1024that is substantially the same as a thickness of PCB 1030. In this case,when the raised portions extend through holes 1032, the main body of theheat sink directly contacts the PCB. Heat is removed directly withouthaving to pass through the PCB.

A dimmer apparatus 1040, shown in FIG. 14, is used for providing adimming functionality to one or more LEDs 1042. Dimmer apparatus 1040can also be connected to a current controller as described above andwill therefore be discussed in conjunction with current controller 910using the same component numbers one shown in FIGS. 10 and 11.

Dimming apparatus 1040 allows LED and cold cathode fluorescent lamps(CFL) to be dimmed in a manner similar to incandescent lighting withoutthe need for expensive and complex circuit components. Dimming apparatus1040 uses a feedback signal 1052 as a function of a source voltage 1054to affect a dimming function that is controlled by a conventionaldimming switch (not shown) through which the source voltage 924 issupplied.

In the present example, LED 914 is connected between capacitor 937 andthe non-inverting input of op amp 1044. A LED current 1046 flows throughthe LED and a sense resistor 1048 to cause the LED to emit light. TheLED current flowing through the sense resistor creates an input voltage1050 at the non-inverting input of op amp 1044. A gain resistor 1056 isconnected between the output and the inverting input of op amp 1044 anda drain resistor 1058 is connected between the inverting input andground 930. Resistors 1056 and 1058 contribute to a voltage 1060 at theinverting input of op amp 1044 and are used for setting the gain of theop amp.

Dimming apparatus 1040 uses resistors 1062 and 1064 arranged in avoltage divider configuration to derive a voltage that is proportionalto source voltage 1054 to add to the inverting input of op amp 1044 tocreate voltage 1060. Resistor 1062 is connected to source voltage 1054and to resistor 1064 which is connected to ground 930. Resistor 1062 and1064 divide source voltage 1054 to create proportional voltage 1068 thatis proportional to source voltage 1054. An optional resistor 1066 isconnected between resistors 1062 and 1064 and the inverting input of opamp 1044. Optional resistor 1066 may be added to separate the functionof dividing source voltage 1054 from the relative effect that it has onthe op amp bias.

The connection of proportional voltage 1068 via resistor 1066 to theinverting input of op amp 1044 causes feedback signal 1052 to bedependent on the level of source voltage 1054. Proportional voltage 1068is reduced when source voltage 1054 is reduced by the conventionaldimmer switch since voltage 1068 is proportional to source voltage 1054.The voltage of feedback signal 1052 increases when input voltage 1060decreases due to a decrease in proportional voltage 1068. Increases inthe voltage of feedback signal 1052 cause an increased voltage atfeedback pin 939 which causes regulator 910 to decrease LED current 1046thereby reducing the brightness level of LED 914. In this manner,decreased line voltage from a conventional dimmer switch causes adecrease in the brightness or lumen output of LED 914.

Dimmer apparatus 1040 does not require the use of a microprocessor andcan be implemented on regulator circuits that lack a brightness control(or enable) function. Other variations of amplifier circuits can be usedto achieve the required voltage or current summing to achieve thedimming function using analog components. The dimmer apparatus can beused in conjunction with the thermal management modifications discussedabove.

While a number of exemplary aspects and embodiments have been discussedabove, those of skill in the art will recognize certain modifications,permutations, additions and sub-combinations thereof. It is thereforeintended that the following appended claims and claims hereafterintroduced are interpreted to include all such modifications,permutations, additions and sub-combinations as are within their truespirit and scope.

1-46. (canceled)
 47. A method of thermal management of an illuminationdevice comprising a light-emitting diode (LED), the method comprising:(a) generating a regulated current from a source voltage; (b) supplyingthe regulated current to the LED; (c) generating a sense voltage basedon (i) the regulated current and (ii) an LED temperature resulting fromheat produced by the LED; and (d) modifying the regulated currentsupplied to the LED based on the sense voltage, whereby the LEDtemperature is maintained within a non-destructive range of LEDtemperatures.
 48. The method of claim 47, further comprising repeatingsteps (b)-(d) at least once.
 49. The method of claim 47, whereingenerating the sense voltage comprises amplifying at least a portion ofthe regulated current, an amplitude of the amplification being based onthe LED temperature resulting from heat produced by the LED.
 50. Athermal-management system for an illumination device comprising alight-emitting diode (LED), the system comprising: means for generatinga regulated current from a source voltage; means for supplying theregulated current to the LED; means for generating a sense voltage basedon (i) the regulated current and (ii) an LED temperature resulting fromheat produced by the LED; and means for modifying the regulated currentsupplied to the LED based on the sense voltage, whereby the LEDtemperature is maintained within a non-destructive range of LEDtemperatures.
 51. The system of claim 50, further comprising means foramplifying at least a portion of the regulated current.
 52. The systemof claim 51, wherein a gain of the amplifying means depends at least inpart on the LED temperature resulting from heat produced by the LED.